1. Field of the Invention
The present invention relates to a multiterminal multilayer ceramic capacitor that is suitable for mounting in a personal computer or other electronic apparatus with a high operating frequency, suitable for surface mounting on a three-dimensional multilayer printed circuit board, and is a low equivalent serial inductance (ESL) and low equivalent serial resistance (ESR) capacitor.
2. Description of the Related Art
In the past, as multiterminal multilayer ceramic capacitors, the capacitor disclosed in U.S. Pat. No. 5,880,925 is known. This capacitor has a capacitor body which has two types of, that is, first and second, internal electrodes and dielectric layers stacked and sandwiched between them. Each of these internal electrodes is formed with a rectangular main portion pattern extending in the longitudinal direction on a face of a rectangular ceramic layer and a plurality of lead patterns extending from the sides of the main portion to the sides of the ceramic layer. The lead patterns of the first internal electrodes and the lead patterns of the second internal electrodes are formed at different positions from each other when seen from a plan view. A plurality of external electrodes are formed at the side faces of the long and short sides of the capacitor body of this multiterminal multilayer ceramic capacitor.
This multiterminal multilayer ceramic capacitor is placed on the surface of a circuit board so that the external electrodes are positioned in a standing direction from the surface of the circuit board. The internal electrodes and the stacking direction of the ceramic layers are substantially vertical to the circuit board. The external electrodes are connected and fixed by soldering to the lands of the circuit pattern of the circuit board so as to mount the capacitor on the surface of the circuit board.
In this multilayer ceramic capacitor, each of the internal electrodes extends thinly in the longitudinal direction of a ceramic layer from one external electrode to another external electrode. There is a long length of overlap of adjoining internal electrodes separated by ceramic layers. Therefore, the inductance component of the capacitor becomes large. Further, the distance between external electrodes facing each other along the longitudinal direction of the capacitor becomes long, so that the circuit pattern forming the circuit board becomes longer and therefore the detouring of the lands becomes longer. This has a detrimental effect on the inductance component.
In addition, in the above multiterminal multilayer ceramic capacitor, since the external electrodes are not provided at the corners of the capacitor body, if supplying reverse voltages to adjoining external terminals, short-circuits sometimes occur at the corners. Further, there is not much space for lead-in below capacitor devices in the design of the lands of the circuit board, mounting discrepancies of the capacitor device are apt to occur at the time of mounting the capacitor.
In personal computers and other electronic apparatuses, however, the operating frequency has increased from 500 MHz to 1 GHz. The power supply circuit requires a low ESL and low ESR multiterminal multilayer ceramic capacitor able to be reliably mounted on a three-dimensional printed circuit board etc. and giving predetermined characteristics.
In the above multiterminal multilayer ceramic capacitor, however, if three-dimensionally mounted on a three-dimensional multilayer printed circuit board etc., the circuit pattern formed on the circuit board becomes longer, the detouring of the lands becomes longer, and there is a detrimental effect on the inductance component. In particular, a circuit pattern comprised of lands at upper positions and lands at lower positions becomes longer, the detouring of the lands becomes longer and has a detrimental effect on the inductance component, and generation of noise becomes unavoidable.
Further, in the above multiterminal multilayer ceramic capacitor, the solder is formed at the external electrodes provided at the side faces of the capacitor body for connection to the lands of the circuit board, the solder formed at adjoining external electrodes easily contact each other and therefore short-circuits easily occur. Further, the conventional multiterminal multilayer ceramic capacitor was not structured suitably for connection to three-dimensionally arranged circuit boards.
Note that as shown in Japanese Unexamined Patent Publication (Kokai) No. 7-169649, Japanese Unexamined Patent Publication (Kokai) No. 7-161568, and Japanese Unexamined Patent Publication (Kokai) No. 8-124800, capacitor arrays of a rectangular or square shape when seen from a plan view have been proposed. These capacitor arrays, however, are made for reducing the crosstalk of capacitive coupling. In these capacitor arrays, while the ends of the external electrodes formed at the side faces of the capacitor body have portions extending out to the top face and bottom face of the capacitor body, the nearby external electrodes similarly extend to the top face and bottom face covering an equal area. Therefore, the structure has not been suited to connection to three-dimensionally arranged circuit boards.
Further, the multilayer capacitor disclosed in Japanese Patent. No. 2657953 is also disclosed. In this capacitor, however, since the external terminals are formed on only the top face and/or bottom face of the capacitor body and external terminals are not formed on the side faces, the external terminals end up being densely concentrated at the top face and/or bottom face of the body. To avoid short-circuits between terminals, the planar area of the body has to be increased.
An object of the present invention is to provide a compact, thin, three-dimensionally mountable multiterminal multilayer ceramic capacitor suitable for mounting in an electronic apparatus with a high operating frequency and suitable for surface mounting on a three-dimensional multilayer printed circuit board, which is a low ESL and low ESR capacitor.
To achieve the object, the multiterminal multilayer ceramic capacitor according to a first aspect of the present invention comprises a ceramic layer; a first internal electrode having a first main portion positioned at the center in a first face of the ceramic layer and having a plurality of first leads extending from sides of the first main portion to sides of the ceramic layer; a second internal electrode having a second main portion which is opposite to the first main portion of the first internal electrode across the ceramic layer and which is arranged in a second face of the ceramic layer opposite to the first face to have the same shape as the first main portion and having a plurality of second leads extending to the sides of the ceramic layer from sides of the second main portion at positions different from the first leads provided at the first internal electrode; first external electrodes formed at side faces of a capacitor body comprised of a plurality of first internal electrodes and second internal electrodes stacked via ceramic layers and electrically connected respectively to the first leads positioned in the same line along a stacking direction of the ceramic layers; second external electrodes alternately formed with respect to the first external electrodes at the side faces of the capacitor body and electrically connected respectively to the second leads positioned in the same line along a stacking direction of the ceramic layers; top pads continuing from top ends of the first external electrodes and extending to a top face of the capacitor body; and bottom pads continuing from bottom ends of the second external terminals and extending to a bottom face of the capacitor body.
The bottom ends of the first external electrodes either do not extend much to the bottom face of the capacitor body or else even if extending are smaller in area than the bottom pads of the second external electrodes. Further, the top ends of the second external electrodes either do not extend much to the top face of the capacitor body or else even if extending are smaller in area than the top pads of the first external electrodes.
Preferably, the first internal electrode is formed with first corner leads extending from corners of the first main portion along the ceramic layer to first corners of the capacitor body; the second internal electrode is formed with second corner leads extending from corners of the second main portion along the ceramic layer to second corners of the capacitor body; first corner external electrodes are formed at the first corners of the capacitor so as to electrically connect to the first corner leads; second corner external electrodes are formed at the second corners of the capacitor so as to electrically connect to the second corner leads; top pads are formed continuing from top ends of the first corner external electrodes and extending to a top face of the capacitor body; and bottom pads are formed continuing from bottom ends of the second corner external electrodes and extending to a bottom face of the capacitor body.
Alternatively, the first internal electrode is formed with first corner leads extending from corners of the first main portion along the ceramic layer to first corners of the capacitor body; first corner external electrodes are formed at the first corners of the capacitor body so as to be electrically connected to the first corner leads; top pads are formed continuing from top ends of the first corner external electrodes and extending to the top face of the capacitor body; and corner leads are not formed at the second internal electrode.
Alternatively, the second internal electrode is formed with second corner leads extending from corners of the second main portion along the ceramic layer to second corners of the capacitor body; second corner external electrodes are formed at the second corners of the capacitor body so as to be electrically connected to the second corner leads; bottom pads are formed continuing from bottom ends of the second corner external electrodes and extending to the bottom face of the capacitor body; and corner leads are not formed at the first internal electrode.
Preferably, the first external electrodes (below, including first corner external electrodes) are connected to a first circuit pattern outside of the capacitor body and the second external electrodes (below, including second corner external electrodes) are connected to a second circuit pattern different from the first circuit pattern.
Preferably, the top pads of the first external electrodes are connected to a first circuit pattern of a top circuit board arranged outside the top of the capacitor body, and the bottom pads of the second external electrodes are connected to a second circuit pattern of a bottom circuit board arranged outside the bottom of the capacitor body.
The nearby external electrodes are for example supplied with voltages of reverse polarities. They may also be supplied with high frequency voltages.
Preferably, the ceramic layer is formed as a square, and the capacitor body is a square when seen from a plan view.
According to the multiterminal multilayer ceramic capacitor according to the present invention, since the distance between external electrodes can be set short, even if mounted on a multilayer board, the total inductance due to the detouring of the lands can be reduced and the lands formed on the multilayer board can be simplified. Further, by supplying voltages of reverse polarities to the nearby external electrodes, current flows uniformly to all of the capacitor body and the magnetic flux is uniformly canceled, so that the ESL can be reduced. As a result, it is possible to realize a low ESL and low ESR capacitor. The capacitor can be suitably used for mounting on a personal computer or other electronic apparatus with a high operating frequency. Further, the capacitor of the present invention is so compact and thin that it is suitable for mounting buried in a three-dimensional multilayer printed circuit board etc.
Further, in the present invention, by connecting the top pads of the first external electrodes to a first circuit pattern of a top circuit board arranged outside the top of the capacitor body and connecting the bottom pads of the second external electrodes to a second circuit pattern of a bottom circuit board arranged outside the bottom of the capacitor body, the capacitor is suitable for three-dimensional mounting. In particular, when only top pads of the first external electrodes are formed at the top face of the capacitor body and when only bottom pads of the second external electrodes are formed at the bottom face of the capacitor body, short-circuits of the first external electrodes and second external electrodes can be effectively prevented.
Further, when the first corner external electrodes and second corner external electrodes are formed at the corners of the capacitor body as well, even if reverse voltages are supplied to the nearby external electrodes, the problem of short-circuits does not arise at the corners. Further, since there is a large space for leading in the lands under the capacitor devices in the design of the lands of the circuit board, it is possible to effectively prevent discrepancies in mounting capacitor devices at the time of mounting.
The multiterminal multilayer ceramic capacitor according to the second aspect of the present invention comprises a ceramic layer; a first internal electrode having a first main portion positioned at the center in a first face of the ceramic layer and having a plurality of first leads extending from sides of the first main portion to sides of the ceramic layer; a second internal electrode having a second main portion which is opposite to the first main portion of the first internal electrode across the ceramic layer and which is arranged in a second face of the ceramic layer opposite to the first face to have the same shape as the first main portion and having a plurality of second leads extending to the sides of the ceramic layer from sides of the second main portion at positions different from the first leads provided at the first internal electrode; first external electrodes formed at side faces of a capacitor body comprised of a plurality of first internal electrodes and second internal electrodes stacked via ceramic layers and electrically connected respectively to the first leads positioned in the same line along a stacking direction of the ceramic layers; and second external electrodes alternately formed with respect to the first external electrodes at the side faces of the capacitor body and electrically connected respectively to the second leads positioned in the same line along the stacking direction of the ceramic layers; the first internal electrode being arranged exposed at a top face of the capacitor body and the second internal electrode being arranged exposed at a bottom face of the capacitor body.
In the multilayer ceramic capacitor according to the second aspect of the present invention, the first electrode itself positioned exposed at the top face of the capacitor body takes the place of the above top pads, while the second electrode itself positioned exposed at the bottom face of the capacitor body takes the place of the bottom pads. Therefore, in the present invention, it is possible to obtain a large area for the electrode pads, three-dimensional mounting of the capacitor becomes easier, and a lower ESL and lower ESR capacitor can be realized.